Genetic counseling: Advanced Maternal Age - Chorionic Villus Sampling (CVS)-3
Advanced Maternal Age - Chorionic Villus Sampling Contracting *Introductions and small talk *Confirm referring obstetrician *Assess understanding for the referral *Elicit concerns and questions *As maternal age increases, we know that the risk for having a child born with a chromosome abnormality also increases. *The reason that we like to see women who are 35 or older is because we can offer testing options *I would like to start today by gathering some medical and family history information so that we can look for any other risk factors that we may need to talk about. **We want to see if there is anything in your history that could pose a risk to this pregnancy Medical/Family History *LMP:_________ *EDC:_________ *Today's gestational age:_________ *How has this pregnancy been going? *Any complications? *Have you had an ultrasound? **Date ________ **Findings:______________ *Anyone in the family have: **Birth defects, SABs, SB, MR, LD, chronic illness, or early cancers? *Tell them what I found; "looks good, it sounds like the pregnancy is going well, I don't see anything that concerns me"* *Do you have any questions? Explanations of Genes and Chromosomes *All pregnancies are at a 3-5% risk of having a baby born with a birth defect. *Women are born with all the eggs that we will ever have, unlike men who continuously make sperm from puberty throughout their lives. *Eggs are stopped in a stage of division until one is ovulated each month. *The older the egg, the more likely a division error might occur. *General *Karyotype *Nondysjunction *Brief natural history of chromosome abnormalities Age Related Risks *Patient's age at delivery: _______ *Risk for Down Syndrome: 1 in ________ ( %) *Risk for any chrom. Abnormality: 1 in ________ ( %) Options *Level II Ultrasound: **High resolution ultrasound **Done at 20+ weeks by an experienced technician ***Better to see more of the developing organs **U/S detection rate for DS is about 60% and for trisomy 18 ~90% **Look for: ***Heart ***Brain ***Shape of the head ***Intestinal problems ***Kidneys ***U/S helps make us suspicious but doesn't give us a yes or no answer. CVS as an Option *Offered between 10-12 weeks *Procedure used to obtain a sample of the placenta from the womb of an expectant mother. *Genetic make-up of placental cells is essentially the same at the fetus since they both come from the same original cell created at conception **When baby is created, the egg splits into two parts: a part that forms the baby and a part that forms the placenta *Analysis can detect many genetic disorders/chromosome abnormalities with 98-99% accuracy **Cannot detect about 90% of birth defects or the severity of a condition Explain Procedure *Transcervical CVS **Only performed from 10-12 weeks **Preferred method if the placenta is posterior and close to the cervix **Sterile speculum is inserted and the vagina and cervix are cleaned with betadeine **By U/S guidance, a thin catheter is guided into the placenta **A syringe is attached and gentle suction is applied to aspirate the villi **Large sample (whole villi) taken **Catheter is removed **NOT recommended for women with a retroverted uterus *Transabdominal CVS **Easiest to perform with anterior or fundal placenta **Abdomen is cleaned with betadeine **A local anesthetic is applied to the skin **By U/S guidance, a needle is guided through the abdominal wall and uterine wall into the placenta (avoid the amniotic sac) **A syringe is attached and gentle suction is applied by the syringe plunger **The needle is moved back and forth with re-direction through the placenta **Small sample (pieces of villi) taken *Procedure takes roughly 5-7 min, after prep time *The sample is examined under the microscope to confirm that fetal tissue has been obtained. (If maternal tissue is present- repeat test). *Following the procedure, the baby's heartbeat will be monitored by U/S *Sample is sent to the lab for results *Direct vs. Culture results: **Direct analysis: A preliminary answer ***Analysis of outer cells which are spontaneously dividing ***Increased rate of error ***Results in 1-2 days ***Few labs do this Culture analysis *Analysis of cells from mesenchymal core *More accurate *Results in 7-14 days *Results differ in about 2% of cases *Results will be reported by ???? Risks of complications *Miscarriage: increased above the background by 1% *Transverse limb reduction defects **Results show that the risk for transverse defects after CVS is ~1 in 3000 (0.03%) **Results show the greatest defects when CVS was performed prior to 10 weeks (limbs are formed at 10 weeks) **How? Suspected that instrumentation interrupts the vascular supply **VUMC has not had any CVS patients who had pregnancies born with limb reductions defects as a result of the procedure. Disadvantages *Risk of laboratory failure *Maternal cell contamination *Mosaicism **Presence of two or more cell lines that differ with respect to their chromosomal constitution **Although the placenta and fetus start out the same, once they diverge- there is a very small chance that the placental cells might have a change that is not changed in the fetal cells - confined placental mosaicism *Insufficient sample obtained *With any of these, follow up is required. **Additional testing Amniocentesis *Also an option, performed from 15+ weeks *Transabdominal removal of amniotic fluid *~ same accuracy, but risks are 1 in 200 for complications. *Tests for NTD's Follow-up *How do you feel about having a CVS? Would you like a few minutes to discuss the option with your partner? *Re-iterate that most babies are born healthy *Will want to do an u/s at about 18-20 weeks- anatomy is big enough to be easily visualized. (looking for structural anomalies) *MSAFP blood test (to detect NTD's) *Elicit final questions and concerns. Notes The information in this outline was last updated in 2001. Material obtained under GFDL Licence from http://en.wikibooks.org/wiki/Handbook_of_Genetic_Counseling